The present invention relates to a method in a communication network for handling temporary identities assigned to terminals connected to the network.
In present cellular systems, a xe2x80x9csubscriber identity confidentiality featurexe2x80x9d is often used for preventing the movements of a subscriber within a communication network to be traced by listening to the signalling over the radio interface. The feature consists of assigning a temporary identity to the subscriber, which identity is changed as often as considered necessary.
It is stated above that the temporary identity is assigned to and associated with the subscriber. However, in many cellular systems the subscription and the terminal are tied together in a way that makes it pointless to make the distinction between the subscriber and the terminal in this context. Hence, in such systems you may as well say that the temporary identity is assigned to and associated with the terminal. It is also possible in a cellular system to have a terminal identity (and a temporary identity replacing this terminal identity) which is completely separated from the subscription. Such a terminal identity may e. g. be used for paging the terminal and for other procedures dealing with setting up a radio bearer and an association between the terminal and the radio access network. In addition, the wordxe2x80x9cuserxe2x80x9d is often used instead ofxe2x80x9csubscriberxe2x80x9d in documents describing procedures in a cellular network. The temporary identities dealt with in this document could be of any of the above three types (i. e. associated with the subscriber (or user), the subscriber and the terminal, or only the terminal). In the previous paragraph the wordxe2x80x9csubscriberxe2x80x9d is used, but in the rest of the document the wordxe2x80x9cterminalxe2x80x9d is consistently used, since this word fits best into a technical description. However, the conclusion of the above is that in all cases the wordsxe2x80x9csubscriberxe2x80x9d orxe2x80x9cuserxe2x80x9d can replace the wordxe2x80x9cterminalxe2x80x9d without changing the applicability of the present invention.
In present systems the temporary identity is only locally unique within a single location area, where a location area is defined as an area within which the terminal or subscriber is able to move around without informing the network of its location. The location areas are used by the network to keep track of the location of a terminal/subscriber. When the terminal is to be contacted by the network, the terminal is normally paged in all cells in the location area.
The local uniqueness allows the temporary identity to be kept short saving radio resources and allows the temporary identities to be locally assigned without co-ordination with the rest of the network. The temporary identity is assigned by a mobile serving node, MSN, responsible for the location area within which the temporary identity is locally unique. A mobile serving node, MSN, is in this context defined as a network node responsible for a certain number of cells in the network creating location areas, and this also implies that a location area may include cells that are controlled by more than one controlling node in the network. Since these controlling nodes may be different in different cellular systems, they will therefore be referred to with this general term Mobile Serving Node, MSN.
In present systems where the subscriber identity confidentiality feature is used a location area can not include cells that are controlled by more than one MSN. Hence, when used in the location area where it was assigned the temporary identity is recognised and translated to the permanent subscriber identity by the responsible MSN. When the temporary identity is used outside the location area where it was assigned, it has to be accompanied by an additional identifier, preferably the location area identity of the location area where the temporary identity was assigned, in order to make it unique and translatable. If the MSN receiving the temporary identity is another than the one that assigned the temporary identity, the accompanying identifier, for example the above mentioned location area identity, can be used to obtain the address of the MSN that can translate the temporary identity to the real subscriber identity.
In most instances, these mechanisms work smoothly since the location area identity is broadcast in all cells, thereby making it possible for the mobile terminal to know when it has entered another location area. However, this also means a lot of signalling in the network consuming precious radio resources.
Temporary identities may also be used if dynamical, customised location areas are used in a network instead of the conventional geographically fixed location areas. One type of dynamical location areas may be location areas created by collecting information regarding the long term and/or short-term historical movements of a terminal. The cells broadcast geographical coordinates, which are used for creating the specific location areas for specific terminals. The location areas thus created are disconnected from the geographical division of the network by the cells. The size or the kind of dynamical location areas may also be dependent on the kind of traffic between the terminal and the network. The general idea behind these dynamical location areas is to minimise the radio resource consumption caused by paging, location updating and periodic registration of a terminal and to distribute the load caused by location updating more evenly between the cells in the network.
Also for this type of location area scheme it has to be possible to identify the MSN that assigned the temporary identity. Even when the permanent subscriber identity is used in conjunction with these location area schemes it has to be possible to identify the MSN used at the previous location update when a location update is performed in a new MSN. The reason for this is that the location area scheme requires that the mobility management context or at least the data associated with the definition of the customised location area is transferred from the previous to the new MSN when the terminal accesses the network in a cell which is controlled by a new MSN. A way to avoid this data transfer between the MSN""s is to send the relevant data (if any) from the MSN to a central database node, for example a Home Location Register (HLR). The necessary data can then be transferred from the HLR to the new MSN at location update in this new MSN. Henceforth, for the simplicity, the possible involvement of a HLR (or similar database node) will be omitted in the description. However, in the above mentioned location area scheme no location area identifiers are broadcast in the cells, only the geographical coordinates of the cells. In addition a location area may well include cells that are controlled by more than one MSN.
In this context, this gives rise to a number of problems/questions:
How should the mobile terminal be identified, when being paged in or when accessing the network? This may be critical when the current cell is not a cell controlled by the MSN that assigned the temporary identity and the temporary identity is only unique in one MSN. Another terminal may have been assigned the same temporary identity by the MSN in control of the current cell.
Should the terminal be made aware of when the previous MSN has to be identified and when consequently the terminal is outside the range of the local uniqueness of its current temporary identity, if a temporary identity is used?
How should the previous MSN be identified, i e the MSN where the data associated with the definition of the previous location area is stored, which may (most likely) or may not be the same MSN that assigned the temporary identity, if a temporary identity is used?
The aim of the present invention is to provide a system with areas within which temporary identities are unique and which areas are without relation to the location areas of a network. The aim is also that within each area, hereafter named uniqueness area, a terminal is provided with a unique temporary identity unique for that specific area. This is obtained with a method for a communication network comprising base-stations and cells forming a geographic service area containing a number of location areas, either geographically fixed location areas or dynamical location areas. The network service area is divided into a number of geographical part-areas, uniqueness areas, which are created and without relation to the location areas.
The uniqueness areas are created so as to fully cover the network service area but not overlapping each other. The uniqueness areas are created from the geographic coordinates broadcast from the cells and geometric definitions of each uniqueness area, e g geometrical shapes. Further, each uniqueness area is provided with an identity, uniqueness area identity, which is unique within the network.
Preferably each uniqueness area is controlled by a single MSN. All MSN""s in the network must know all MSN""s responsible for each uniqueness area.
The merits of the invention are that it uncouples the area of local uniqueness for the temporary identity from the network structure. This means that the uniqueness areas can be based on other criteria, like for example attempting to have on average the same number of users in each area. Thus, location areas and temporary uniqueness areas are not tied to each other. Having uniqueness areas without relation to the location areas is necessary when the customised (i.e. a unique location area for each terminal), dynamic location areas are used.
The invention also allows a great flexibility in the uniqueness area definitions and easy redefinition. By using the geographical information from the cells and geometric definitions, uniqueness areas of almost arbitrary shape can be made. Because this information is provided to the terminal it can keep track of when it enters a new uniqueness area, thus keeping precious radio traffic as low as possible.
In conjunction with dynamical location area schemes, the invention solves the problem of identification of mobile terminals and also the retrieval of the mobility management context at location: update.